1. Field of the Invention
The present invention relates, in general, to a time slot allocation apparatus and method for preventing collisions between time slots in a Time Division Multiple Access (TDMA)-based Radio Frequency Identification (RFID) network, and, more particularly, to a time slot allocation apparatus and method for preventing collisions between time slots in a TDMA-based RFID network, which can rapidly transmit a minimum number of time slots to RFID readers while eliminating interference between the RFID readers in the TDMA-based RFID network.
2. Description of the Related Art
Generally, Radio Frequency Identification (RFID) is a non-contact type recognition system for transmitting and processing information about objects or surrounding environments using a small-sized semiconductor chip, and is predicted to be the technology that will replace barcodes, because direct contact and scanning are not required.
Further, an RFID network is configured such that identification codes required to identify objects or animals having RFID tags attached thereto are received through communication between a plurality of RFID readers and a plurality of RFID tags, and such that the identification codes are collected and filtered through RFID middleware and are transmitted to a central server, and data about the objects or animals can be obtained on the basis of the data about the identification codes stored in a database.
In this case, in order to conduct communication between RFID readers present in an RFID network and RFID tags, frequency collisions must be prevented from occurring. Frequency collisions can be classified into frequency collisions occurring between RFID readers, and frequency collisions occurring between RFID readers and an RFID tag, and are described with reference to the attached drawing.
FIG. 1 is a diagram showing interference between RFID readers and interference between RFID readers and an RFID tag, occurring in an RFID network. As shown in FIG. 1, each RFID reader receives data about an RFID tag placed within the radius of the RFID reader in which the radio waves of the RFID reader can be reached, in the RFID network.
Further, since a plurality of RFID readers driven through the above operation is present in the RFID network, the case where, when an arbitrary RFID reader transmits radio waves and reads an identification code included in an RFID tag, the transmitted radio waves may reach another RFID reader, may occur. This case is shown in (a) in FIG. 1.
Meanwhile, since a plurality of RFID readers driven through the above operation is present in the RFID network, the case where, when two RFID readers transmit radio waves and read an identification code included in the same RFID tag, frequency interference occurs, and thus the RFID readers cannot accurately read the identification code, may occur. Such a case is shown in (b) in FIG. 1.
As described above, interference with RFID readers, such as interference between RFID readers, or a collision occurring when a plurality of RFID readers simultaneously attempts to connect to the same RFID tag, is commonly called a collision between RFID readers.
In order to solve this collision, a method of randomly allocating time slots to RFID readers, and a method of randomly allocating time slots to prevent the occurrence of interference while minimizing the number of time slots allocated to each RFID reader, may be used.
The former allocation method is configured to allocate different time slots to all RFID readers, and the latter allocation method is configured to allocate time slots to RFID readers so as to prevent all RFID readers from interfering with each other while changing the time slots of RFID readers in which interference occurred.
However, the former allocation method is problematic in that, since different time slots are designated, the number of time slots increases, and the scanning period of RFID readers is lengthened, thus the performance of sensing the movement of RFID tags is deteriorated. In addition, the latter allocation method is problematic in that, since random time slots are designated in RFID readers in which interference occurred, a time slot must be designated again when the same time slot is randomly designated, so that the time taken for trial and error is increased, and an optimal solution cannot be found.